This grant application is designed to study the mechanism of gonadotropin interaction with testicular receptors as related to the concepts of testicular activation and desensitization. Our primary objective is to determine whether gonadotropin binding is related to "receptor occupancy" or to its "loss" via dissociation of loosely coupled receptors from adenylate cyclase at the membrane level. According to our working hypothesis, we envision "receptor loss" as one of the mechanisms associated with the activation of the adenylate cyclase which in turn leads to the adenylate cyclase inactivation when the process of receptor depletion from the broken cell preparations is completed. To study this phenomenon in greater detail and to further differentiate between the processes of receptor dissociation and receptor synthesis in intact tissue, we propose to investigate the patterns of gonadotropin receptor depletion and replenishment in vivo following a single or multiple physiologic doses of hCG, hLH, hFSH, and aqueous ethanol. Six parameters to be quantitated are gonadotropin receptor sites, the adenylate cyclase activity, serum gonadotropins, total cAMP contents, steroidogenis output, and ethanol-soluble factor activities. The integration of these results, along with those of in vitro studies to replenish gonadotropin receptors following their complete depletion under optimal conditions by agents such as prolactin and other hormones through perifusion technique, should provide the first direct evidence of de novo receptor synthesis and its translocation at the membrane level. In perifusion experiments all six parameters will be measured to establish the criteria for receptor synthesis, translocation, and dissociation. Furthermore, the binding model that we had already proposed will be supported by studies on cAMP-cAMP protein kinase system. We shall attempt to purify ethanol-soluble factors (i.e. receptors) in order to convert inactive adenylate cyclase into an active cyclase and we shall attempt to characterize the soluble factors as a prerequisite to study of their biosynthesis. We have proposed to use hCG, hLH, and hFSH for these studies and we state that the methodologies required for these studies are available in this laboratory.